1. Field of the Invention
The invention relates to image processing, and more particularly, to a method and apparatus for suppressing repetitive high-frequency information in a video data stream.
2. Description of the Prior Art
In video surveillance situations, it is oftentimes desirable to monitor a number of remote locations, such as entrances and exits of a building or stations along a production line, from a centralized monitoring location. For these situations, separate video cameras are stationed at each respective location to produce a view of the monitored location.
Video images are made of pixels arranged in a two-dimensional array. A pixel is a spot on a screen in a specified location which has luminance component that represents the brightness or darkness of the pixel. In color video images, the pixel also has information as to the color of that pixel in addition to the luminance information. The pixel information for a video image can be represented as digital information or data.
Video images may be transferred over a transmission medium, such as the Internet, for remote monitoring. Because the amount of data in a video image is large, it may take a long time to transfer the video image data.
The video image data can also be stored in a memory or on a disk in a video image file. The stored video image file may be retrieved later for subsequent viewing. Video image files use large amounts of storage space in the memory or disk.
Video image compression has been used to reduce the amount of data making up the video image. However, some images have a large amount of detail. Such detail is associated with a pixel sequence that has many large increases and decreases in the luminance of the pixel values in a short period of time, and will be referred to as high-frequency data or high-frequency portions of the image. The changes in the luminance of the pixel values may appear as edges or lines in the image. The high-frequency portion of the image may have repetitive and non-repetitive portions. For instance, a pattern may be repeated in a large part of the image. Such a repetitive pattern may occur when a person in the image is wearing a shirt with vertically oriented pin-stripes. The pin-stripes in the shirt have a large amount of repetitive high-frequency information. Even after compression, the region of the image having the repetitive high-frequency information can occupy a large portion of the data making up the video image.
One technique to reduce the amount of video image data applies a low pass filter to the entire image. However, applying the low pass filter to the entire image also affects any non-repetitive highly detailed portions of the image, in addition to the repetitive high-frequency portions. As a result, this technique tends to blur the image.
Therefore, a method and apparatus that suppresses the amount of repetitive high-frequency information in an image is needed. This method and apparatus should also preserve any non-repetitive highly detailed, that is, high-frequency, portions of the image.